An intracranial aneurysm is a weak region in the wall of an artery in the brain, where dilation or ballooning of the arterial wall may occur. Histologically, decreases in the tunica media, the middle muscular layer of the artery, and the internal elastic lamina cause structural defects. These defects, combined with hemodynamic factors, lead to aneurismal out-pouchings. Intracranial aneurysms are quite common diseases with a prevalence ranging from one to five percent among adult population according to autopsy studies. In the US alone, ten to twelve million people may have intracranial aneurysms.
Current methods for treating intracranial aneurysms include surgical clipping and endovascular coiling. In the surgical clipping method, the skull of the patient is opened, and a surgical clip is placed across the neck of the aneurysm to stop blood from flowing into the aneurysm sac. The risk of this method is relatively high, especially for elderly or medically complicated patients. Endovascular coiling procedure is a less invasive method involving placement of one or more coils, delivered through a catheter, into the aneurysm until the sac of the aneurysm is completely packed with coils. It helps to trigger a thrombus inside the aneurysm. Although endovascular coiling is deemed to be safer than surgical clipping, it has its own limitations. First, after the aneurysm is filled with the coils, it will remain its original size. As a result, the pressure on the surrounding tissue exerted by the aneurysm will not be removed. Second, this procedure is effective for the aneurysm that involves a well-formed sac with a small neck. When used to treat the wide-neck aneurysm, the coil is likely to protrude into the parent vessels. A solution to prevent coil protrusion is to use a stent in combination with coiling embolization. In the stent-assisted coiling procedure, a stent is first placed across the aneurysm neck, serving as a scaffold inside the lumen. Then, the coils are delivered into the sac of the aneurysm through the interstices of the stent. Although this method can solve some problems of purely coiling, it still has some drawbacks. First, a microcatheter through which the coils are sent into the aneurysm sac has to be navigated through the interstices of the stent. This process is difficult and time-consuming. Second, the coils are still used to fill the sac of the aneurysm. As a result, the aneurysm size remains the same after the treatment. Furthermore, when it comes to the pseudoaneurysm where no fully-formed aneurysm sac can be identified, coiling methods are not applicable.
Using a stent alone to treat the aneurysm is a promising way to avoid the problems stated above. In this method, a stent with an area of coverage is placed across the aneurysm neck, blocking it sufficiently to restrain blood from flowing into the sac and finally to trigger a thrombus within the aneurysm. Because the aneurysm solidifies naturally on itself, there is no danger of its rupture. Furthermore, because no coil is involved in this method, the aneurysm will gradually shrink as the thrombus is absorbed. Consequently, the pressure applied on the surrounding tissue can be removed. The reason why this method has not used is because of the difficulty in designing the stent. It has to be flexible enough to pass through and morph to the very tortuous blood vessels in the brain while at the same time providing sufficient coverage to shut the aneurysm. Current stents made for the stent-assisted coiling, such as Neuroform stent (Boston Scientific), LEO stent (Balt) and Enterprise stent (Corids), have a very open design to allow the coils to pass through the interstices. They do not provide much coverage at all. Therefore, they are inadequate for direct treatment of the aneurysm. PED (ev3) and SILK stent (Balt) are currently two dedicated flow diverters under clinical trials. However, they have their own limitations mainly because both stents are braided stents, which do not provide much radial strength. Besides, use of these stents may cause blockage of branch blood vessels.
It is an object of the invention to at least partially address one or more of the shortcomings described above in relation to the prior art.